NICE MOVE!
Funny story -- when my father was young (in the early 60's), he had a buddy who was SO proud of his car and the mileage it got. As a joke, my dad and a buddy snuck over to the guy's house every night for a week and dumped in a couple of gallons of gas. The guy was BRAGGIN so much about the magnificent mileage he was getting.
Well, then they reversed course and started siphoning a couple of gallons OUT each night. The guy wasn't quite so "enthusiastic" about things after that. In fact, they had to ASK him about his mileage -- he just looked at the ground and mumbled something like "I just can't figure it out..."
They NEVER let him in on the little game they had been playing with him.
Straight from an episode of 'Married With Children'.